Way to increase/decrease velocity while retaining orbit?

[Wigw2]

Title says it. I\'m trying to dock to another ship, just as practice for deep space recovery, But the velocity at a 200km orbit seems to be pretty much locked at 2100m/s. Is there a way, Even with a plugin or something, For me to speed up or slow down the velocity on an orbit without drastically changing altitude (Under 100m altitude difference would be stellar.)

Any tips, My fellow kerbals?

[Mr_Orion]

This is impossible in real life.

[SteevyT]

The way to speed up or slow down is to change the size of your orbit. Larger orbits are slower, smaller orbits are faster, so to catch up with something ahead of you, you need to slow down so you drop into a smaller orbit.

[UmbralRaptor]

For a circular orbit, speed at a given altitude is constant. It\'s a bit more complicated with elliptical orbits, but again speed and altitude are directly related.

For an orbital rendezvous, you\'ll want to have one ship a bit higher (slower) or lower (faster) orbit, for them to meet up. Depending on where they are right now, this may take a while.

[socket7]

Physics doesn\'t work that way.

Velocity IS locked to orbital altitude.

The common way to meet up with another object in orbit is to time your launch so you end up in orbit at the same altitude and velocity.

Once you are in the same orbit, If you are trailing behind your target, you lower your ships orbit a bit. The lower orbit will make your ship go faster then your target, and slowly bring your closer to it. If you are ahead of your target, you raise your orbit, and your ship will slow down, allowing the target to catch up to you.

It can take a VERY, VERY long time if you don\'t spend some time figuring out how to time your launches to put you somewhere close to where you want to be.

Orbital maneuvering is very counter intuitive. At times you might need to burn away from your target to get closer to it.

Also, Mechjeb does have tools to assist you in these sorts of things.

[Wigw2]

The more I play this game, The more I feel like I should take a day or 2 and learn about real world orbital mechanics and advanced physics.

Thanks anyways, Guys.

[Vanamonde]

Well, there is kind of a way to do it, but mostly in theory because I don\'t think you can be precise enough to do it in practice. Put yourself in the orbit you want but going too fast, point your nose straight toward the center of the planet, and burn precisely enough to prevent your altitude from rising, while continually altering attitude to stay pointed at the center of the planet. In effect, you\'re artificially increasing the gravity of the planet to make your chosen velocity the proper one for an orbit of that altitude.

But the one time I tried it was a miserable failure, because of course being even a little bit off either on throttle or attitude means drastically cumulative effects to your total velocity.

[UmbralRaptor]

The more I play this game, The more I feel like I should take a day or 2 and learn about real world orbital mechanics and advanced physics.

It\'s very worth doing. And fun. (You get to pull off things that are sort of like being in an early Heinlein story)

[Cykyrios]

The only way to change your speed while maintaining your orbit (more or less), and this can only make you accelerate, is to simulate a higher gravity by burning directly towards Kerbin (or whatever you\'re orbiting) after having gained some horizontal speed (you\'d want to burn horizontally and slowly point down).

Needless to say, this is a very fuel-consuming thing to do, with very limited benefits. And it\'s also pretty difficult to perform.

Best thing would be to learn how to do orbital rendezvous to get within 5 km of the target, from where you can roughly burn towards it - not too much, though.

[Cryphonus]

Mathematically impossible. However there is a single trick you can do, you can burn retro and lower your velocity and keep your same orbit by constantly burning to your RAD+(pitch 90 degrees). This will work as much as you can burn in the upwards direction.

[VincentMcConnell]

The more I play this game, The more I feel like I should take a day or 2 and learn about real world orbital mechanics and advanced physics.

A day or two is definitely not enough. And what you\'re describing in the OP goes against the laws of orbital mechanics.

[Endeavour]

The more I play this game, The more I feel like I should take a day or 2 and learn about real world orbital mechanics and advanced physics.

I\'ve learned more info that is real-life applicable in this game than in any other game I have ever played. It has inspired me to research, and the research helps.

[Stevenator1]

The more I play this game, The more I feel like I should take a day or 2 and learn about real world orbital mechanics and advanced physics.

Thanks anyways, Guys.

Well, considering what you want to do is mathematically impossible, there are other ways to pull off a rendevouz. One of my favorite ways, I shall detail for you:

Get in the same orbit (or as close as you can). You do not have to be anywhere near the same position as your target.

Do a burn in the direction of your velocity vector for a few seconds, pushing your Apoaxis out a few kilometers. This will make your orbit so that only the place you currently are will be in line with the orbit of the object you are trying to reach. The rest of the orbit will be farther out.

Now turn on your warp. Because your orbit is now slightly longer than your object, you will take just a little bit longer to do every rotation around the orbit. You will notice that every time you 'lap' your orbit back to the point where the orbit of your object and yourself line up, your object will be just a little bit closer to you.

When it is extremely close, do a retrograde burn at that orbital intersection point to put yourself back in the same orbit as the object.

And now you are damn close to your object, and can do small orbital tweaks if needed to get to it.

[duckunlimited2]

Ooooooh! Pick me! Pick Me!

You should do what I do:

*assuming both crafts have the same orbits (or as close as possible)

Step 1. retrograde; how much is up to you. However, more does equal a faster rendezvous, but it will take more fuel. Less is slower but you use less fuel and its more precise.

Step 2. After step 1, your craft will be slower than your rendezvous point/craft/thingy, so it will catch up to you, however, you will also be dropping altitude, to prevent that THRUST UP PERIODICALLY. up as in pointing your engine nozzle at the ground and thrusting away from kerbin/mun/sun/minmus/etc. If you actually look at the orbital map while your doing this burn, you will see that the immediate front half of your orbit will be raised up and the immediate back half of your orbit will be lowered. So burn 'up' to keep your immediate orbital path within altitude.

Step 3. When your crafts are within 10-200 meters away from each other, boost/prograde to fix your orbit and keep pace with the craft.

This method is best used when you need to cover a large distance quickly, or if you don\'t have a lot of time to wait for a hundred of orbits to happen (i.e. while in kerbol orbit)

enjoy

[Ydoow]

Everyone here is wrong, technically speaking.

You CAN increase your orbital speed at a given altitude.

That is, 200km orbit is NOT locked at ~2100m/s

Right now, I can just see everyone freaking out at me lol

The reason a ship seems locked at ~2,100m/s at 200km is because of gravity.

Gravity is relatively the same when it comes to low altitude orbits (the ISS experiences gravity ~9.81m/s², the same as the ground. If you don\'t understand this, you should research why. Learning is fun!)

Imagine having an eraser tied to the end of a rubber band.

Gravity DOES change the farther you go out, as does a rubber band\'s stretchiness force the farther you stretch it; the farther out you are, the rubber band (gravity) pulls back differently than if you were closer.

Spinning the eraser at 2,100m/s makes your eraser extend to 200km orbit.

Now what happens if you slow down to 2,000m/s?

Your orbit decreases because you\'re exerting less force outward (centripetal force), and thus the rubber band will pull you inward slightly.

It\'s the same with gravity. Gravity is kinda like a giant rubber band with your craft being the eraser.

Okay, so now you can see that slowing down/speeding up will ultimately change the force you\'re exerting outward, and thus change your altitude.

So how can you speed up/slow down without changing your altitude?

Simple! It comes down to forces.

Instead of a rubber band, imagine a firm piece of string.

Now spin it at 2,000m/s, and then 2,100m/s.

The string won\'t expand/contract at either speed (at least not noticeably).

Why?

The string can increase/decrease the force it exerts without changing it\'s length up until you spin it so fast, that the force required to keep that eraser on the string snaps the string itself (hyperbolic trajectory).

So all of this is to say:

If you can add another force vector (directional force) that ADDS to gravity, you would therefore have to increase your speed to maintain your orbital altitude.

tl;dr or didn\'t understand

Attach a rocket that points directly towards the center of kerbin (acting with gravity) and increase your rockets speed. Assuming you somehow manage to get the thrust proportions right, you can go faster and maintain orbital altitude.

Also, yes, you should learn about real life physics/mechanics to play this game to it\'s full potential.

The math isn\'t quite so important, but the concepts are.

Also, shame on everyone else for thinking this was impossible.

This is the founding idea behind LaGrange points!

[VincentMcConnell]

As soon as you stop thrusting radially towards Kerbin, your velocity will change based on your orbit. Nice try, though, Ydow.

[Ydoow]

As soon as you stop thrusting radially towards Kerbin, your velocity will change based on your orbit. Nice try, though, Ydow.

Well yeah, just retro-burn to bring your speed back to 2,100m/s

It still works. It\'s just ungodly complex and requires precision that\'s probably impossible to achieve in KSP

[duckunlimited2]

It still works. It\'s just ungodly complex and requires precision that\'s probably impossible to achieve in KSP

I agree that it still works, but I disagree that its complex and requires perfect precision in order for it to work in ksp. All you have to do is thrust down in order to keep your altitude. Boom! That\'s it. It\'s not complex at all! And you don\'t have to persistently keep burning down in order to keep a perfect altitude. Just periodically burn down for a couple of seconds to keep it 50-200 meters in range of your target altitude. And remember, our end goal is to rendezvous, so we don\'t have to do it forever and prove we can break the rules of physics.

Its doable. In fact, this method is my choice method for a rendezvous. Also, if you look at my previous post ( which should be 4 post before this post) I detailed how I do it. (actually its not exactly the same, since I set it up to slow the craft, not speed it up, but it works both ways with minor tweaking)

[Ydoow]

I agree that it still works, but I disagree that its complex and requires perfect precision in order for it to work in ksp. All you have to do is thrust down in order to keep your altitude. Boom! That\'s it. It\'s not complex at all! And you don\'t have to persistently keep burning down in order to keep a perfect altitude. Just periodically burn down for a couple of seconds to keep it 50-200 meters in range of your target altitude. And remember, our end goal is to rendezvous, so we don\'t have to do it forever and prove we can break the rules of physics.

Its doable. In fact, this method is my choice method for a rendezvous. Also, if you look at my previous post ( which should be 4 post before this post) I detailed how I do it. (actually its not exactly the same, since I set it up to slow the craft, not speed it up, but it works both ways with minor tweaking)

Well, it\'s not exactly breaking physics, just exploiting it.

You\'re right, I guess you don\'t have to be precise. I was thinking of a constant burn to perfectly counter-act your centripetal force.

You could just do periodic downward thrusts.

The issue is that Engine control is pretty limited in KSP right now.

i.e. It\'s hard to alternate between two engines burning and 1 engine burning/idling

[duckunlimited2]

The issue is that Engine control is pretty limited in KSP right now.

i.e. It\'s hard to alternate between two engines burning and 1 engine burning/idling

I can do it with one engine if the craft is small and spins around quickly enough. If that fails, RCS is your friend.

[shikarirock]

Use a gimballed engine and mechjeb, order mechjeb to keep your desired altitude and uncheck the kill horizontal velocity box. You should do this after you\'re going at your desired speed though. If all goes well, mechjeb will burn towards Kerbin.

You will use up a lot of fuel fast and you won\'t be able to warp past 2x though.

[maltesh]

Use a gimballed engine and mechjeb, order mechjeb to keep your desired altitude and uncheck the kill horizontal velocity box. You should do this after you\'re going at your desired speed though. If all goes well, mechjeb will burn towards Kerbin.

You will use up a lot of fuel fast and you won\'t be able to warp past 2x though.

If you\'re using MechJeb, you might as well use the Rendezvous Computer\'s sync orbits capability. Put your periapsis on the target\'s orbit, wait to reach it, and burn to put yourself at that point at one of the three future times that the target will be there. Kill relative velocity when you\'re both there, and then close the distance.

[Kosmo-not]

Everyone here is wrong, technically speaking.

Did you bother to read Vanamonde\'s post?

[Endeavour]

Did you bother to read Vanamonde\'s post?

Wow. I completely missed that. Ydoow\'s wall of text must have distracted me.

[Ydoow]

Did you bother to read Vanamonde\'s post?

Yes. Yes I did not.

Honestly, I missed his post. I read through most of them as I was scrolling, but I guess I missed his D:

mah bad